The present invention relates to a process for the production of planar structure thin film magnetic heads and to a head obtained by this process.
Two types of thin film magnetic heads are known, namely those mounted perpendicular to the magnetic film to be read or recorded and those mounted parallel to said film.
FIG. 1 shows a head formed from two pole pieces P1 and P2 defining an air gap E, a coil B surrounding said pole pieces. The recording film C passes in front of air gap E. Such a head is described in Japan patent abstracts, vol. 5, No. 150, P-81, 822 of 22.9.1981.
The field gradient produced by such a head is high and produces intense demagnetizing fields in the recording film, which makes writing difficult. Moreover, on reading, a signal V is obtained like that of FIG. 2. Perpendicular to the external angles of the pole pieces voltage polarity reversals appear, which leads to serious problems in connection with the processing of the information read.
For these reasons, preference is given to the use of horizontally mounted heads, like that shown in FIG. 3. Such a head is described in European patent application 85400136.9, published under No. 0 152 326. It is possible to see a first magnetic film 1, in which is formed a coil 2 and a second magnetic film 3 subdivided into two parts by an amagnetic spacer 4. A hard film 5 protects the assembly and ensures the planarity of the film.
FIG. 4 illustrates a known process for the production of a horizontal head. This process is produced in Japan patent abstracts, vol. 5, No. 5, P-44, 677, of 14.1.1981. On a substrate 6 is deposited a first magnetic film M1, followed by an insulating film 7 and a coil B (part a). This is followed by the depositing of an insulating film 8 and the etching of two wells P1, P2 (part b). This is followed by the deposition of a second magnetic film M2, which comes into contact with the first as a result of the two wells P1 and P2 (part c). This is followed by the formation of an air gap, the deposition of a glass layer (part d) and the planification of the assembly (part e).
Although satisfactory in certain respects, these prior art processes and means suffer from disadvantages. In the case of the head of FIG. 3, there are still outer ends of pole pieces which can lead to reversing of the reading signal. In the process illustrated in FIG. 4, the fineness or thinness of the end of the pole pieces is avoided, but the air gap is open and relatively wide, being gradually filled with magnetic particles, which magnetically short-circuit the head. Finally, the magnetic flux produced by the coil follows a quasi-constant section circuit and consequently there is no flux concentration at the air gap. Moreover, in the process of FIG. 4, coil B is not in a single plane, instead being in two separate planes, one corresponding to the central part above the first pole piece and another lower plane corresponding to the two side parts (only one of which is shown to the right in FIG. 4, i.e. part a). The lateral parts make it possible to close the winding around the pole pieces. Moreover, it can be seen that pole piece M1 is not buried in the substrate 6, which leads to a head having a large relief. Finally, the parts of the pole piece M2 not covered by the protective film 9 are very wide (because they are substantially as wide as the coil), which makes the head very fragile.